With the prospective emergence of the All Electric Airplane, in which all functions and services are performed electrically, the flight-control surfaces will be operated by some type of electromechanical actuator system (EMAS). Typically, such an EMAS will interface with a quad-redundant fly-by-wire (or fly-by-light) system that will furnish command information to the EMAS, while the flight control system computers being in turn responsible for the management of the EMAS and the airplane's flight characteristics.
In the past, and in most current large airplanes, the control surface actuator function is performed with hydraulic jacks or cylinders. In the event of a hydraulic supply failure (or a failure in the closed loop servo control or a stuck servo-valve etc.) in such systems the hydraulic ram can be bypassed to permit other actuators, connected to the same surface, to continue operation. In the case of the EMAS, however, there is concern that a broken-tooth in a gear-train may cause a mechanical-jam or that a bearing seizure may make it impossible for other (redundant) actuators to drive the control surface. Presently, there is no such simple method to bypass or free-wheel the jammed actuator.
Prior examples of attempts to solve this problem include U.S. Pat. No. 2,441,247 "Mechanical Translating Device" by A. W. Mooney who discloses an electrically powered actuator rotatably mounted to the aircraft structure. Rotation of the actuator is normally prevented by a circular gear mounted to the actuator which is in engagement with a worm gear. Thus, in normal operation, rotation of an output shaft can be accomplished because the worm gear prevents the actuator from rotating. Should the actuator fail, however, the worm gear can be rotated manually or by any other drive means, thus still providing an effective output.
The problem with this actuation system is that if redundancy is required, i.e., two separate actuators controlling the same control surface, there is no means to automatically disengage a failed actuator, since the worm gear cannot be back driven, effectively preventing the actuator from rotating.
Another patent of interest is U.S. Pat. No. 3,950,686 "Series Redundant Drive System" by James C. Randall. Here a plurality of motors are mechanically connected in series so as to provide operational redundancy. The shaft of a given motor is rigidly attached to the housing of the next motor in the series so that rotation of the first shaft will cause the coupled motor and its shaft to rotate. While this system will provide effective operation should one motor fail, the output shafts are held in position by means of the magnetic attraction between the rotor and poles. This does not provide for a positive lock on the position of the control surface connected thereto.
Still another patent of interest is U.S. Pat. No. 4,289,996 "Actuators" by R. R. Barnes et al. Here a pair of motors are coupled to a differential gear assembly which in turn drives a screw assembly attached to the load (a control surface). A lock mechanism is provided on each motor which will lock the motor and prevent its output shaft from rotating should failure of the other motor occur. This allows the other motor to continue to drive the control surface through the differential gear assembly. This system requires that each motor be coupled together by a differential gear assembly. Should the differential gear assembly fail, both motors become ineffective.
Other patents of interest relating to redundance control systems for aircraft control surfaces are U.S. Pat. No. 3,790,108 "Redundant Stabilizer Control" by J. W. Bock; U.S. Pat. No. 2,315,110 "Control Apparatus for Aircraft" by C. Dornier; U.S. Pat. No. 2,491,842 "Actuator System" by B. A. Wells; U.S. Pat. No. 2,549,815 "Servo Unit" by W. L. Huntington; U.S. Pat. No. 3,140,843 "Servo System" by R. H. Pettet; and U.K. Pat. No. 576,797 "Improvements in Electric Motor Drive Units" by C. Heal. None of these fulfills the objectives of the subject invention.
In the field of hydraulic couplings, of interest is U.S. Pat. No. 2,422,545 "Regulating Means for Washing Machine Agitators" by V. Hanson. While this patent relates to washing machines which are far afield from the subject invention, it does disclose a pertinent hydraulic agitator. A hydraulic cylinder is disclosed having a rotatable blade mounted therein which divides the cylinder into two portions. A passageway is provided between the two portions with a valve located therein which can be used to disconnect communications therebetween. While on the surface this hydraulic cylinder is similar to one of Applicant's embodiments, there are significant differences. The primary difference is that an air passage is provided between the blade mounting sleeve and the top and bottom walls (webs), insuring that there is not an airtight fit at either of these points. This is necessary in the Hanson design because the cylinder is sequentially filled and drained of water during the wash cycle and there must be provisions allowing the air to escape. Thus, this device would not be applicable to Applicant's system in that zero leakage between the portions of the cylinder divided by the blade or the exterior of the cylinder is allowable because in normal operation, the blade reacts against the fluid to provide torque transmittal. Furthermore, in the preferred embodiments of Hanson, a fill hole is left open allowing some fluid to be forced out during rotation of the blade. Here again, this would be totally unacceptable on Applicant's actuator assemblies herein disclosed.
Other hydraulic couplings of interest are U.S. Pat. No. 3,182,470 "Sealing Device" by G. N. Smith; U.S. Pat. No. 3,283,537 "Impulse Tool with Bypass Means" by R. P. Gillis; U.S. Pat. No. 1,630,737 "Coupling" by W. B. Flanders; U.S. Pat. No. 1,224,669 "Hydraulic Clutch" by W. L. Rounds; U.S. Pat. No. 3,653,228 "Progressive Clutch" by G. Tiberio; U.S. Pat. No. 2,304,907 "Hydraulic Clutch and Control Mechanism" by C. C. Goodson et al.; U.S. Pat. No. 2,034,021 "Power Transmission Device" by W. S. Brian; U.S. Pat. No. 1,685,839 "Torque Equalizing System" by A. D. Du Bois; U.S. Pat. No. 1,510,368 "Hydraulic Coupling and Change Speed Gear" by S. G. Wingquist; U.S. Pat. No. 3,113,469 "Rotary Viscous Fluid Damper" by A. E. Farr et al.; and U.S. Pat. No. 2,010,366 "Grinding Machine" by B. A. Kearns.
Therefore, it is a primary object of the subject invention to provide an actuation system for primarily controlling the position of a control surface of an aircraft while providing at the same time a means wherein a jammed or disabled actuator can be effectively bypassed to allow other actuators connected to the same control surface to function freely.
It is another object of this invention to provide an actuation system for controlling the position of a control surface of an aircraft wherein a hydraulic coupling is mounted between the actuator and the control surface of the aircraft and which can be used to decouple a jammed or disabled actuator from the control surface. Said hydraulic coupling provides the additional feature of viscous damping.
Another object of the subject invention is to provide an actuation system wherein the hydraulic coupling is efficiently packaged with the actuator by use of an annular hydraulic cylinder with the actuator mounted therein.